Alphaviruses comprise a set of serologically related arthropod-borne viruses of the Togavirus family. Briefly, alphaviruses are distributed worldwide, and persist in nature through a mosquito to vertebrate cycle. Birds, rodents, horses, primates, and humans are among the defined alphavirus vertebrate reservoir/hosts.
Twenty-six known viruses and virus subtypes have been classified within the alphavirus genus utilizing the hemagglutination inhibition (HI) assay. Briefly, the HI test segregates the 26 alphaviruses into three major complexes: the Venezuelan encephalitis (VE) complex, the Semliki Forest (SF) complex, and the western encephalitis (WE) complex. In addition, four additional viruses, eastern encephalitis (EE), Barmah Forest, Middelburg, and Ndumu, receive individual classification based on the HI serological assay.
Members of the alphavirus genus are also classified based on their relative clinical features in humans: alphaviruses associated primarily with encephalitis, and alphaviruses associated primarily with fever, rash, and polyarthritis. Included in the former group are the VE and WE complexes, and EE. In general, infection with this group can result in permanent sequelae, including behavior changes and learning disabilities, or death. In the latter group is the SF complex, comprised of the individual alphaviruses Chikungunya, O'nyong-nyong, Sindbis, Ross River, and Mayaro. With respect to this group, although serious epidemics have been reported, infection is in general self-limiting, without permanent sequelae.
Sindbis virus is the prototype member of the alphavirus genus of the Togavirus family. Although not usually apparent, clinical manifestations of Sindbis virus infection may include fever, arthritis, and rash. Sindbis virus is distributed over Europe, Africa, Asia, and Australia, with the best epidemiological data coming from South Africa, where 20% of the population is seropositive. (For a review, see Peters and Dalrymple, Fields Virology (2d ed), Fields et al. (eds.), B. N. Raven Press, New York, N.Y., chapter 26, pp. 713-762). Infectious Sindbis virus has been isolated from human serum only during an outbreak in Uganda and in a single case from Central Africa.
The morphology and morphogenesis of the alphavirus genus is generally quite uniform. In particular, the enveloped 60-65 nm particles infect most vertebrate cells, where productive infection is cytopathic. On the other hand, infection of invertebrate cells, for example, those derived from mosquitoes, does not result in any overt cytopathology. Typically, alphaviruses are propagated in BHK-21 or vero cells, where growth is rapid, reaching a maximum yield within 24 hours of infection. Field strains are usually isolated on primary avian embryo, for example chicken fibroblast cultures (CEF).
The genomic RNA (49S RNA) of alphaviruses is unsegmented, of positive polarity, approximately 11-12 kb in length, and contains a 5′ cap and a 3′ polyadenylate tail. Infectious enveloped virus is produced by assembly of the viral nucleocapsid proteins onto genomic RNA in the cytoplasm, and budding through the cell membrane embedded with viral-encoded glycoproteins. Entry of virus into cells appears to occur by endocytosis through clatherin-coated pits, fusion of the viral membrane with the endosome, release of the nucleocapsid and uncoating of the viral genome. During viral replication, the genomic 49S RNA serves as template for synthesis of a complementary negative strand. The negative strand in turn serves as template for full-length genomic RNA and for an internally initiated positive-strand 26S subgenomic RNA. The nonstructural proteins are translated from the genomic RNA. Alphaviral structural proteins are translated from the subgenomic 26S RNA. All viral genes are expressed as polyproteins and processed into individual proteins by proteolytic cleavage post-translation.
The use of recombinant virus vectors (in particular, alphavirus vectors) to treat individuals requires that they be able to be transported and stored for long periods at a desired temperature, such that infectivity and viability of the recombinant virus is retained. Current methods for storing recombinant viruses generally involve storage as liquids and at low temperatures. Such methods present problems in Third World countries, which typically do not have adequate refrigeration capabilities. For example, each year in Africa, millions of children die from infectious diseases such as measles. Vaccines necessary for the prevention of these diseases cannot be distributed to the majority of these countries because refrigeration is not readily accessible.
In addition to storage as liquids and at low temperatures, present viral formulations often contain media components that are not desirable for injection into patients. Consequently, there is a need in the art for a method of preserving purified recombinant viral vector (and in particular, alphavirus vectors) in a lyophilized form at elevated temperatures, and for this form to be suitable for injection into patients.
The present invention discloses recombinant alphavirus vectors which are suitable for use in a variety of applications, including for example, gene therapy, and further provides other related advantages.